Floating grid gates



Jan. 8, 1963 T. A. COFFEE 3,072,852

FLOATING GRID GATES Filed Feb. 11, 1960 2 Sheets-Sheet 1 w N 2' u. o: aI: E E m m f E f 8 2 3 t g m "J n m o 0 w 2% g 5 l i 8 w 00 a CD gThomas A.Coffee 1 LLI LL! 0 O m 2% I g o o (D (0 Jan. 8, 1963 T. A.COFFEE 3,072,852

FLOATING GRID GATES Filed Feb. 11, 1960 2 Sheets-Sheet 2 (INPUT FROMSOURCE [6) l GATE I CONDITIONING-J PULSES [INPUT FROM SOUIRZCE 17) I I ICONTACT POTENTIAL\ (GRID VOLTAGE) CUTOFF POTENTIAL A l3 (OUTPUT OF FIGJ)l4 (OUTPUT OF FIG.2)

FIG. 3

Thomas A. Coffee,

INVEN TOR.

X .W BY

United States 3,072,852 FLGA'IING GRID GATES Thomas A. Cofi'ee, LasCruces, N. Mere, assignor to the United States of America as representedby the Secretary of the Army Filed Feb. 11, 196i), Ser. No. 8,202 6Claims. Cl. 328-94) (Granted under Title 35, U.S. Code (1952), sec. 266)The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment of royaltythereon.

This invention relates generally to electron tube circuits, and moreparticularly to a floating grid electron tube circuit.

In the usual practice of the art, electronic devices which depend uponmaintaining a certain bias point in their operation are very critical inadjustment and are adversely effected by aging variations in signalinput and power supply fluctuations. It is, therefore, highly desirableto obtain a circuit which is stable in time despite signal variations,and power supply changes; and it would be further highly advantageous tohave such a circuit self-adjusting. Accordingly, it will be seen thatthis invention fulfills these needs in many applications.

A general object of this invention is to provide a device which utilizesan input signal to produce a determining potential usable in themodification of input signals.

It is a more specific purpose of this invention to provide aself-adjusting highly stable coincidence circuit.

It is a further object of this invention to provide a self adjusting,self-determined highly stable gate circuit.

In accordance with this invention an electron tube device is constructedutilizing a positive-signal-developed negative grid potential bias tocontrol electron flow between a negative cathode and a positive plate,the control potential being, by its nature, of such a magnitude as topermit the passage of only a determined portion of further signals. Thegrid is connected to one or more sources through isolating capacitance,and having no direct ground return path. The device may have a cathodeload, a plate load, or both. A pulse, positive with respect to cathode,when coupled between the input side of the grid capacitance and cathode,will cause the capacitance to draw grid current until the capacitancebecomes charged. This charge, which will equal in magnitude the voltagepotential of the input pulse, will remain as a negative bias on the gridfor a period which is limited only by the insulating properties of thecapacitance and associated electron tube. In effect, the positive peakof the input signal (a composite signal if more than one signal is used)is clamped to contact bias (floating grid bias without signal) and theoutput of the tube responds to that part of the signal extending fromthe positive peak of the signal downward, in a negative direction, in anamount equal in magnitude to cutoff bias for the particularcathode-anode potential employed. The cutoff point of the tube will thenserve to clip any portion of the bottom of the signal which extendsbelow cutoff. In the case in which two or more simultaneous signals arepresented, the bias value is approximately equal to the negative sum ofthe positive value of signal one plus signal two, etc. for as manysignals as are presented. In this case one signal may be used to raisethe grid level up to cutoff, thus allowing the other signal or signalsto be fully reproduced. This type of action is commonly referred to asgating in the concerned art.

These and other features and objects of this invention will be morereadily understood from the following description read in conjunctionwith the drawings in which:

FIGURE 1 is a schematic diagram showing a general purpose form of theinvention;

3fi7252 Patented Jan. 8, 1963 FIGURE 2 is a schematic diagram showing asecond, more specialized form of the invention.

FIGURE 3 shows certain coincident waveforms as are found at certainplaces in an embodiment of the invention;

FIGURE 4 shows a third embodiment of the invention.

From FIGURE 1, it can be seen that electron tube 3 is a conventionaltriode, having grid 4, emitting cathode 5 and anode 6, said anode beingconnected to an anode load resistance 7. Connected to the grid 4 arecapacitances 8 and 9. FIGURE 2 shows the same configuration of theinvention with the exception that anode load 7 has been omitted andcathode load it has been substituted. The circuit inputs are representedby waveforms 11 and 12, in both figures, while waveform 13 representsthe output of the circuit in FIGURE 1, and 14 represents the output ofthe circuit shown in FIGURE 2. FIGURE 3 gives a simultaneousrepresentation of the signal input to be gated, 11, the gating pulse 12,the grid voltage 2t), and the output 13 of the circuit of FIGURE 1.

In operation, the tube 3 draws current from the oathode 5 through theanode 6 and the load resistor 7. A positive signal 11 from source I6 iscapacitively coupled to grid 4 via capacitor 8 causing the grid tobecome positive with respect to the cathode. Electrons are immediatelydrawn from the cathode 5 to the grid 4 and to the plate 6. Current flowsand the signal 11 from source 16 appears in the output of tube 3. Sincethere is no fixed or applied bias (the circuit having no D.C. path fromgrid 4- to ground) a cathode 5 to grid 4 electron fiow will take placeduring conduction of the tube until the tube reaches its natural stateof equilibrium, at which time the grid will have stabilized at thecontact potential point of the tube (normally just positive +0.2 to +0.7volt). The tube will continue to conduct after reaching contactpotential and the signal 11 from source .16 will continue to appear inthe output.

If another positive signal 12 from source 17, is simultaneousiy yetnon-coincidentally applied to grid 4 via capacitor 9, then both thesignals from source 16 and 17 will appear in the output withoutnoticeable change in the tubes operation. Electron flow from cathode 5to grid 4- will have once again occurred until the grid 4 is stabilizedat the contact potential of the tube.

When a first coincidence of signals from source 16 and source 17 occursthe additive effect of the simultaneous positive potentials on bothcapacitors 3 and 9 causes the grid 4- to again go positive with respectto cathode 5. Again electrons flow from cathode 5 to grid 4 as the tubeconducts and the grid 4 again stabilizes at contact potential as itspositive charge is mostly neutralized by electrons flowing from thecathode.

Since this electron flow from cathode 5 to grid 4 which occurs when thetube is conducting, is not reversible, removal of the coincidentalexistance of signals from sources 16 or 17, or both will not affect thenegative charge on grid 4 (now equivalent to the sum of the signals 11and 12) which will hold the tube so far below cut-off that neithersignal 11 nor 12 applied alone, nor together but not in coincidence, cancause the tube to conduct. After the first coincidence only a furthercoincidence will appear as a signal in the output 13, hence gatingaction occurs.

FIGURE 2 shows an embodiment in which a cathode output is utilized inorder to obtain a positive pulse, rather than the negative pulseobtained from the circuit of FIGURE 1.

FIGURE 4 shows a circuit in which the signals are applied via only onecapacitor 15 and wherein the internal impedances of the two signalsources 16 and 17 are represented by resistances R and R respectively.Operation is, in this case, identical with the foregoing,

with the ex eption that the signals are combined previous to theirapplication to the capacitor.

Those skilled in the art will appreciate that the objects oi thisinvention are met by the utilization of a novel floating grid vacuumtube circuit in an unusual mode of operation. It will be furtherappreciated by those skilled in the art, that the device set forthherein provides a more stable, highly dependable coincidence circuitthan has been heretofore possible.

The principle of the invention explained in connection with specificexemplification thereof will suggest many other applications andmodifications of the same. A partial list of these would includeamplitude selection, diode switching for position signals, timeselections, multigrid switching, multiple coincidence operation,adjacent time selection, time demodulation, and sync separation. Most ofthese applications, and others for which the present invention may beadvantageously employed, are treated in volume 19 of the RadiationLaboratory Series, particularly chapter 10. It is accordingly desiredthat, in construing the breadth of the appended claims, they shall notbe limited to the specific details shown and described in connectionwith exemplifications thereof.

Therefore what is claimed and it is desired to secure by Letters Patentof the United States is:

I claim:

1. An electron tube circuit comprising a vacuum tube having at least oneanode, at least one cathode and at least one grid, said anode beingconnected through an impedance element to a source of voltage positivein relation to said cathode, said grid being direct current isolatedfrom said anode and said cathode, a capacitive input element connectedto said grid, a pair of signal sources being connected in parallelbetween said cathode and said input element.

2. An electron tube circuit comprising a vacuum tube having at least oneanode, at least one cathode, and'at least one grid, said anode connectedto a source of voltto a source of voltage positive in relation to saidcathode, a capacitor connected to said grid, a signal source, a controlpotential source, said grid being direct current isolated from saidanode and said cathode, said grid being connected through a parallelconnection of said signal source and said control potential source tosaid cathode.

4. An electron tube circuit comprising a vacuum tube having at least oneanode, at least one cathode and at.

least one grid, said anode being connected to a source of voltagepositive in relation to said cathode, said grid being direct currentisolated from said anode and said cathode, a plurality of signal sourcesand a plurality of capacitors, each of said sources being connected tosaid cathode and through separate said capacitors to said grid.

5. A circuit comprising a vacuum tube having a grid, a cathode, and ananode, a pair of capacitors connected in parallel and to said grid, saidgrid thereby being direct current isolated from said cathode and saidanode, a pair of pulsing sources each connected between a respective oneof said capacitors and said cathode, a sub stantially constant voltagesource, and a resistance connected between said constant voltage sourceand said anode, whereby an output signal proportional to one of saidpulsing sources and-controlled by the other of said pulsing sources isdeveloped across said resistance.

6. A circuit comprising a vacuum tube having agrid, a cathode and ananode; a voltage source; a plurality of pulsing means and a plurality ofcapacitors connected in parallel lines between said grid and saidcathode, each of said lines including one of said pulsing means and oneof said capacitors said grid thereby being direct current isolated fromsaid anode and said cathode; and a resistance connected in series withsaid voltage source, said.

anode, and said cathode; whereby an output signal proportional to one ofsaid pulsing means and controlled by the other of said pulsing means isdeveloped across said resistance.

References Cited in the file of this patent UNITED STATES PATENTS2,549,764 Bartels Apr. 24, 1951 2,575,708 Glick Nov. 20, 1951 2,823,307Freas et a1. Feb. 11, 1958 OTHER REFERENCES Seely: Electron-TubeCircuits, McGraW-Hill, 1950, pages 402-3.

1. AN ELECTRON TUBE CIRCUIT COMPRISING A VACUUM TUBE HAVING AT LEAST ONEANODE, AT LEAST ONE CATHODE AND AT LEAST ONE GRID, SAID ANODE BEINGCONNECTED THROUGH AN IMPEDANCE ELEMENT TO A SOURCE OF VOLTAGE POSITIVEIN RELATION TO SAID CATHODE, SAID GRID BEING DIRECT CURRENT ISOLATEDFROM SAID ANODE AND SAID CATHODE, A CAPACITIVE INPUT ELEMENT CONNECTEDTO SAID GRID, A PAIR OF SIGNAL SOURCES BEING CONNECTED IN PARALLELBETWEEN SAID CATHODE AND SAID INPUT ELEMENT.